RFR: 8343622: AesDkCrypto.stringToKey should not return null [v3]

[Weijun Wang]

> When an exception happens inside these stringToKey() methods, it returns a null. This would lead to unexpected NPE some time in the future.

Weijun Wang has updated the pull request incrementally with one additional commit since the last revision:

  add cause to exception

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21908/files
  - new: https://git.openjdk.org/jdk/pull/21908/files/8ed39e88..48af1a25

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21908&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21908&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21908.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21908/head:pull/21908

PR: https://git.openjdk.org/jdk/pull/21908